1. Field of the Invention
The present invention relates generally to a rupture disc assembly having a bi-directional, concavo-convex rupture disc and a support body for the rupture disc that is provided with a generally V-shaped cutting element in plan view and disposed to engage and sever the disc when the disc is deflected toward the cutting element. The cutting element has a pair of leg components that are connected to the interior wall surface of the support body and that converge and join at their innermost extremities. In particular, the V-shaped cutting element is of one-piece construction with the central V-shaped cutting edge section of the cutting element defined by a unitary crease in the cutting element being positioned to extend into the concave portion of the rupture disc. The cutting edge of the cutting element includes cutting edge segments that extend along the full length of each of the leg components of the cutting element, and that are arcuate along the longitudinal length of each leg component.
The holder member for the bi-directional rupture disc having a unitary, one-piece V-shaped cutting element, which is particularly useful for sanitary processes and equipment in food, beverage, and pharmaceutical applications, meets current third-party industry approved 3A sanitary standard 60-00. The V-shaped cutting element opens a significantly greater initial area than obtained with three-blade knife structure.
2. Description of the Prior Art
There has long been a need for reliable reverse buckling rupture disc assemblies that open at predictable positive and negative pressures. This is especially true in the pharmaceutical industry where the valuable content of a process vessel must be protected from cyclic vacuum conditions that could cause contamination of the contents of the vessel, or result in an expensive shutdown of the vessel and interfere with the overall manufacturing process. Specifications for protection of processes often require that a safety device such as a rupture disc be capable of rupturing to release pressure in a vessel when the positive pressure in the vessel exceeds a predetermined protective value. That same disc, however, must also protect against relatively small negative pressure conditions imposed on the process contents and thereby the protective rupture disc. The single disc must control against dangerous overpressures, and at the same time reverse and open under minimal vacuum conditions in order to protect the process vessel and its contents.
For example, in certain applications, the process specifications require that a protective disc reverse and open fully under a vacuum condition as little as one inch of water imposed on the convex face of the disc. At the same time that disc must be capable of resisting rupture at a relatively high positive pressure on the concave face of the disc.
In order to assure full opening of a disc under a specified vacuum, it has been the practice to provide a holder for the disc which includes a knife blade located on the concave side of the disc so that upon reversal of the disc in response to a vacuum condition, the disc is severed by the knife and desirably opens fully. A number of different knife blade configurations for assuring opening of a concavo-convex disc have been proposed, with some achieving substantial commercial acceptance. One such knife blade design is shown and described in U.S. Pat. No. 4,119,236 of Oct. 10, 1978. In the '236 patent, the cutting member is in the form of a triangular knife having radially extending knife blade sections that terminate in a central knife blade edge. The angle between adjacent knife blade sections is the same, i.e., 60°.
Because the knife of the '236 patent is made up of three separate angularly disposed knives, the knives must be welded at their zones of joinder. This means that there is a residual weld fillet along the width of each of the adjacent knife blades. These weld fillets are believed to be in part responsible for what is deemed to be the unacceptable failure rates of discs to open upon reversal and engagement with the tri-knife cutting member. Rupture discs used with tri-knife blades of the '236 patent type that are designed for use in sanitary food and pharmaceutical production facilities generally employ a relatively thin, flexible rupture disc of Teflon® or the like as a barrier disc. Teflon is a tough synthetic resin material that can resist timely and required extent of severing if a significant area of the disc is not immediately cut accompanied by a rapid rate of propagation of the sever lines.